Ring opening tandem

The third group of reactions is termed C3-C5 tandem difunctionalization (96JA5672,98JA509). Protonation of 3 (X = O, R = R = R = H) with triflic acid in methanol causes ring opening and formation of the tmns-14 and d.s-4-methoxy-... 

Selective transformations Selective styrene ring opening [103] One-pot domino process for regioselective synthesis of a-carbonyl furans [104] Tandem process for synthesis of quinoxalines [105] Atmospheric oxidation of toluene [106] Cyclohexane oxidation [107] Synthesis of imines from alcohols [108] Synthesis of 2-aminodiphenylamine [109] 9H-Fluorene oxidation [110] Dehydrogenation of ethane in the presence of C02 [111] Decomposition of methane [112] Carbon monoxide oxidation [113]... 

Addition of alkyllithium to cyclobutanones and transmetallation with VO(OEt)Cl2 is considered to give a similar alkoxide intermediates, which are converted to either the y-chloroketones 239 or the olefinic ketone 240 depending on the substituent of cyclobutanones. Deprotonation of the cationic species, formed by further oxidation of the radical intermediate, leads to 240. The oxovanadium compound also induces tandem nucleophilic addition of silyl enol ethers and oxidative ring-opening transformation to produce 6-chloro-l,3-diketones and 2-tetrahydrofurylidene ketones. (Scheme 95)... 

Scheme 6.9. Tandem Zr-catalyzed kinetic resolution and Ru-catalyzed ring-opening/ring-closing metatheses afford chiral chromenes with high optical purity.

Scheme 60 Mechanism for titanocene-catalyzed epoxide ring opening and tandem reaction...

A formal transfer of a furan ring was achieved by the tandem intramolecular Diels-Alder reaction and base-catalyzed ring-opening of the adduct [136]. 

A tandem ring-opening of 3,4- and 3,6-dilithiated thienothiophenes has been used to synthesize polyfunctionalized enediynes (e.g. Scheme 9). ... 

The structural diversity (and complexity) of the products obtained by the MCR between tertiary isocyano amides, aldehydes, and amines could be increased to various heterocyclic scaffolds by combining the initial 2,4,5-tiisubstituted oxazole MCR with in situ intramolecular tandem processes (Fig. 17). Most tandem processes reported are based on the reactivity of the oxazole ring toward C=C or C=C bonds in hetero Diels-Alder reactions followed by ring opening reactions generating the rather complex heterocyclic products with high degrees of variation. 

Pahnans et al. prepared 5 by the reaction of [RuCl2(p-cymene)]2 and 2-phenyl-2-aminopropionamide in the presence of potassium carbonate. They used 5 in an iterative tandem catalysis for the synthesis of chiral oligoesters. The enzymatic ring opening of 6-methyl-e-caprolactone was combined with ruthenium-catalyzed alcohol racemization to produce optically active oligomers of 6-methyl-e-capro-lactone [23] (Scheme 1.17). 

Perfluoroalkylated epoxides as representatives of alicyclic ethers are successfully oxidized152 directly to a-hydroxycarboxylic acids 5 despite the fact that the epoxides 4 are protonated and subsequently hydrolyzed with difficulty. It has been found that the tandem ring opening/oxi-dation reaction is accomplished by concentrated nitric acid152 in the presence of copper ions in the mixture.181... 

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